1. Field of the Invention
This invention relates to complexes useful in the formation of stabilizer additives for halogen-containing polymers such as polyvinyl chloride (PVC).
Metal salts of organic acids complexed with β-diketone compounds, such as calcium benzoate 1,3-diphenylpropane-1,3-dionate (CBDBM), are useful in the formulation of stabilizers for halogenated resins and, when used jointly with other low toxic intermediates, such as zinc or magnesium intermediates, can form effective stabilizers with low toxicity and better performance than other known stabilizers, including those containing toxic heavy metals such as cadmium and lead. Pursuant to the present invention, these stabilizer complexes are prepared utilizing a Claisen condensation reaction and precipitation with water and heptane.
2. Description of the Related Art
Halogen-containing resins, particularly polyvinyl chloride resins, are inherently unstable to heat and decompose through a dehydrohalogenation reaction at the time of processing, when exposed to high temperature, or upon exposure to sunlight, etc. The result of this decomposition includes discoloration, degrading of mechanical properties, and other objectionable changes in the physical properties of the finished product.
Attempts have been made to improve the thermal stability of halogenated resins by adding stabilizers such as metal salts of organic acids, inorganic basic metal compounds, organotin compounds, organic phosphites, epoxy compounds or β-diketones thereto. Stabilizers ensure satisfactory thermal stability during processing at high output rates.
Many stabilizers used in the past contained barium, cadmium and/or lead. Due to their toxicity, there is a strong interest in replacing these heavy metals with non-toxic stabilizers, such as those containing calcium and zinc. Non-toxic stabilizers that have been used include combinations of organic acid zinc salts, organic acid alkaline earth metal salts, organotin compounds, organic phosphite esters, epoxy compounds, antioxidants, polyols, etc. Among these non-toxic stabilizers, potassium, calcium or magnesium salts of organic acids have been used as a fundamental stabilizer for halogenated resins.
Although stabilizers comprising potassium, calcium or magnesium salts of organic acids are effective in avoiding fast degradation of a halogenated resin over a prolonged period of time insuring good long term stability, they are less effective with respect to discoloration, particularly discoloration in the initial stage of heating.
β-diketone compounds are known co-stabilizers in the presence of zinc compounds which overcome objectionable discoloration of halogenated resins. Methods for producing β-diketones are also known in the art. For example, U.S. Pat. No. 4,482,745 discloses a method for synthesizing 1,3-diphenyl-1,3-propanedione by reacting acetophenone with methyl benzoate in the presence of calcium oxide. The 1,3-diphenyl-1,3-propanedione may then be utilized to produce herbicidal agents such as 1,2-dimethyl-3,5-diphenylpyrazolium methyl sulfate.
β-diketones are also used in conjunction with zinc carboxylates in a series of chlorinated polymer stabilizers.
For example, U.S. Pat. No. 5,756,570, the contents of which are incorporated by reference herein, discloses an electrical grade polyvinyl chloride resin composition which avoids the use of lead-based stabilizers. U.S. Pat. No. 5,756,570 discloses many heat stabilizers that exclude cadmium and lead and includes epoxides, salts of monocarboxylic acids (including zinc salts), phenolic antioxidants, organic phosphates, and β-diketones.
U.S. Pat. No. 4,252,698, the contents of which are incorporated by reference herein, provides an anti-yellowing additive for PVC resins which includes at least one overbased sulfonate or phenolate compound of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, titanium, aluminum, zirconium, or tin, and a 1,3-diketone compound having 5 to 30 carbon atoms or a lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, aluminum, tin or zirconium salt thereof. Other stabilizers may also be employed with the stabilizer composition disclosed in the '698 patent to improve the overall effectiveness of the final stabilizer composition.
In addition, U.S. Pat. No. 5,880,189, the contents of which are incorporated by reference herein, discloses liquid PVC stabilizers and lubricants which are barium-zinc carboxylate salt mixtures.
U.S. Pat. No. 6,362,264, the contents of which are incorporated by reference herein, discloses a stabilizer for food contact and medical grade PVC that contains about 10-40 parts by weight of a zinc carboxylate, about 50-80 parts by weight of an alkyl ester of thiodipropionic acid and about 5-20 parts by weight of a phenolic antioxidant.
The non-toxic stabilizers noted above have certain disadvantages. The most significant disadvantage is their lower efficiency, as demonstrated by their unsatisfactory early color. The lower efficiency of calcium/zinc stabilizers results in a higher cost than lead or barium/zinc stabilizers because they require expensive additives as antioxidants, radical scavengers and others.
Moreover, the use of halogenated resins has recently become more diversified and thus the processing conditions and the environment for their use have become more and more severe, which makes the stabilizing effect of known stabilizers insufficient.
Thus it would be desirable to utilize a stabilizer system for a halogenated resin whereby the heat stability of the halogenated resin can be improved avoiding discoloration with greater efficiency utilizing non-toxic stabilizers.